With increasing power density in electronics packages/modules, thermal resistances at multiple interfaces are a bottleneck to efficient heat removal from the package. In this work, the performance of thermal interface materials such as grease, thermoplastic adhesives and diffusion-bonded interfaces are characterized using the phase-sensitive transient thermoreflectance technique. A multi-layer heat conduction model was constructed and theoretical solutions were derived to obtain the relation between phase lag and the thermal/physical properties. This technique enables simultaneous extraction of the contact resistance and bulk thermal conductivity of the TIMs. With the measurements, the bulk thermal conductivity of Dow TC-5022 thermal grease (70 to 75 μm bondline thickness) was 3 to 5 W/(m•K) and the contact resistance was 5 to 10 mm 2 •K/W. For the Btech thermoplastic material (45 to 80 μm bondline thickness), the bulk thermal conductivity was 20 to 50 W/(m•K) and the contact resistance was 2 to 5 mm 2 •K/W. Measurements were also conducted to quantify the thermal performance of diffusion-bonded interface for power electronics applications. Results with the diffusion-bonded sample showed that the interfacial thermal resistance is more than one order of magnitude lower than those of traditional TIMs, suggesting potential pathways to efficient thermal management.

Thermal management for electric machines is important as the automotive industry continues to transition to more electrically dominant vehicle propulsion systems. With the push to reduce component size, lower costs, and reduce weight without sacrificing performance or reliability, the challenges associated with thermal management for power electronics and electric machines increase. The transition to more electrically dominant propulsion systems leads to higher-power duty cycles for electric drive systems. Thermal management of electric machines directly improves power density and reliability; however, it is a significant challenge because heat transfer and fluid flow in electric machines are complex. Thermal management is one path to improve the performance, efficiency, cost, and the sizing of electric machines to operate within thermal constraints.

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